Pulp

I looked into this and there's a problem. Removing the BaseDistribution model forces us to create the migration that cleans up the base distribution table.

However, this migration causes all previous migrations that touch the base distribution table in anyway to fail:

django.db.migrations.exceptions.InvalidBasesError: Cannot resolve bases for [<ModelState: 'file.FileDistribution'>, <ModelState: 'rpm.RpmDistribution'>]                                     

This is pretty much any migration involving distributions and it includes the migrations we created to move the data from the base distribution table to the distribution table. We can use run_before to solve this problem but there are two things to consider.

First, we've already released plugins that are compatible with pulpcore 3.13. So we'd have to postpone removing BaseDistribution until at least 3.14. We could still remove BaseDistribution stuff from the plugin API though in 3.13.

Second, let's say we ship the base distribution removal migration in 3.14. In order to support 3.14, plugins will declare their that migrations run_before this new migration but doing so will mean that these plugins won't work against 3.13 as run_before checks for the migration, and this new migration won't be in 3.13 (see previous paragraph).

What we could do is either:

1. Create a no-op migration in 3.13 that plugin migrations could pin to via run_before
2. Use an arbitrary migration that proceeds the base distribution removal migration (e.g. 0063_repository_retained_versions)

Thoughts?

PR: https://github.com/pulp/pulpcore/pull/1303

Today at pulpcore, we agreed to target 3.14 with this work.

Adding back to 3.13 to discuss at next go/no-go meeting.

Applied in changeset pulpcore|aed355fbc380a13a4a767e2627cbd54c7ff8f107.